The present invention pertains in general to a device for making a denture mold which is utilized in dental techniques for making teeth prostheses. More specifically the invention relates to a supporting plate into which a prosthesis or model material to be hardened is filled.
Supporting plates for dental devices have been disclosed in applicant's U.S. Pat. Nos. 4,371,339 and 4,608,016.
A supporting plate comprising two portions has been disclosed, for example in DE-PS No. 28 56 963corresponding to U.S. Pat. No. 4,283,173. One of the portions is a cheek-side portion and another is a tongue-side portion. These portions are connected to each other by a plurality of webs. These two portions have side walls facing each other and defining a groove of the shape of the dental arch and forming guiding surfaces for a model tooth stump. The portion of the supporting plate and the webs are made of one-piece from a rigid plastic. The distance between the opposing side walls of two portions is constant and unchangeable due to the webs which connect the side walls of the two portions of the supporting plate at the shortest distance.
Studies have shown that dental models manufactured with such supporting plates have not been sufficiently precise to meet the requirements of modern dental practice. Measurements by the microscopes have proven that with such dental models it has not been possible to set individual model teeth stumps, after the sawing up operation, back to the initial position in the supporting plate. Gypsum expands during its hardening whereby this expansion has a negative effect on the model in the direction transversal to the direction of elongation of the tooth arch while the expansion in the direction of elongation is compensated for by a saw clearance, particularly when the tooth arch is divided into many portions. By the expansion of individual tooth stumps transversely to the direction of elongation of the dental arch the distance between two guide surfaces is increased so that individual sawn portions or model tooth stumps can not be adjusted relative to each other in height in the groove which is conically widens in the known supporting plate, and the distance between the side walls limiting that groove remains unchanged due to the use of a formstable plastic, and is also smaller than the distance between the guide surfaces after the hardening of the model material.
To eliminate the disadvantage of an incorrect height relations between individual tooth stumps, the tooth stump has been often pressed into the groove with a substantial external effort whereby a slightly smaller expansion has been obtained at the front teeth region of the dental arch than at the back teeth area. This has caused a deformation of the model tooth stump which affected the precision of the denture model.
Moreover, with the use of conventional supporting plates, a play-free guidance of individual tooth stumps has been achievable so that a precise initial positioning or repositioning of individual tooth stumps was not ensured.